The present invention relates to a timepiece including a movement mounted in a casing ring, a dial mounted above the ring, a crystal mounted above the dial and means for securing the crystal onto a case.
Several documents describe ways of mounting the aforecited elements in relation to each other.
Swiss Patent No. CH 499 813 concerns a device for fixing a watch movement in its case. This document indicates that in order to secure the dial, it can be held by step fitting its outer periphery in a notch of the casing ring. As this known device has the drawback of being ill suited to modern assembly line production, the document cited proposes a dial provided with lugs allowing the dial to be centred, the dial being introduced into a notch arranged in the top part of the casing ring. In order to allow centring, the ring also has, in its top part, recesses corresponding to the lugs of the dial. Thus, in this embodiment, angular positioning and accurate centring of the dial is obtained with respect to the ring. However, no means are indicated which allow the crystal to be angularly positioned and centred with respect to the dial, since the crystal simply rests in a notch of a middle part-bezel.
European Patent No. EP 0 549 978 discloses a timepiece including means for the angular positioning of a crystal on a case. These angular positioning means are formed, on the one hand, by a notch arranged directly in an edge of the crystal and, on the other hand, by a projecting portion which is directly arranged on the middle part of the case and which is engaged in said notch. By bringing the crystal onto the middle part and by rotating the notch and projecting portion until they coincide, they engage angularly with each other and the crystal is eventually secured to the case. Here too, although using means which are close to those which will be described hereinafter, there is no question of positioning the crystal angularly with respect to the dial.
It will further be mentioned that welding the dial by means of three studs emerging from the casing ring is known from certain Swatch (registered trade mark) watches. There again, there is no question of orienting and centring the crystal with respect to the dial.
German Patent No. DE 70 04 514 U discloses a mutual mounting of a dial and a case for a timepiece. In one embodiment, the crystal is provided with a shoulder under which are integrated projecting portions of cylindrical shape. These projecting portions pass through first holes made in the dial, then second holes made in the case to be driven finally into sleeve tubes. It goes without saying that this construction allows the crystal to be angularly positioned and centred with respect to the dial and with respect to the case. However, it will be observed that this mounting system is cumbersome because of the space which it requires lengthways. It should also be noted that the purpose of this system is to secure the crystal onto the dial, then onto the case but not to orient it with respect to these components. As will be seen in the following description, the crystal according to the present invention is secured to the case by other means than those which orient it with respect to the dial.
The necessity of centring and angularly positioning the crystal with respect to the dial exists in numerous circumstances two of which will be provided here by way of example.
If the movement has a date ring whose figures appear in turn behind a window arranged in the dial and if the crystal has a lens for enlarging these figures, it is clear that it is imperative that the lens is located exactly opposite the window. This requires very precise positioning of the crystal with respect to the dial.
If the hour index or the figures indicating the hours are transferred onto the inner wall of the crystal, it is also clear that the dial on which the hands rotate has to be carefully positioned with respect to the crystal. The transfers applied to the crystal could also be various signs or a trade mark, and thus very precise positioning of the crystal with respect to the dial is required.
In the case of the aforecited Swiss Patent No. CH 499 813, manual intervention is required to orient the crystal properly with respect to the dial. In the case of the aforecited European Patent No. EP 0 549 978, since the crystal is oriented with respect to the case, it is the dial which would have to be able to be oriented with respect to the case. One can well imagine that such manual orientation is not suited to the automatic assembly of a timepiece. Finally, in the case of the German Patent No. DE 70 04 514, if such orientation of the crystal with respect to the dial exists solely because of the need to secure the crystal on the case, the construction proposed is complicated, expensive and cumbersome.
In order to answer these requirements, the timepiece according to the present invention is characterised in that the dial includes at least one lug projecting from its flank and in that the crystal is provided with an annular shoulder resting on the dial and a collar surrounding the flank of said dial, this collar being provided with at least one hollow arranged so as to cap said lug in order position angularly and to centre the crystal with respect to the dial.